The present invention relates to a method of forming a gate line and gate electrode of a liquid crystal display (LCD), a method of forming a data line and source/drain electrodes of a LCD, and a method of manufacturing a TFT array substrate of an LCD.
Due to characteristics such as light weight, thinness, and low power consumption, an LCD is developing as a display of the next generation. Also, an LCD emits no radiation. Liquid crystal molecules with optical anisotropy are interposed between an array substrate and a color film substrate, and images are displayed with change of the refractive index upon application of electrical field. Due to superior display quality and high definition, an active matrix LCD is becoming widely used. A thin film transistor (TFT) as an active switch element is included in each pixel of the active matrix LCD, which utilizes one of the terminals for ON/OFF control and another terminal as a common electrode.
FIG. 1 is a top view showing a conventional array substrate. FIGS. 2a-2e are cross-sectional views taken along line A-A in FIG. 1, showing each stage in the process for fabricating the conventional array substrate.
The array substrate comprises a back-channel etch bottom-gate TFT, a pixel electrode 10, a gate line 1, and a data line 5. The TFT comprises a gate electrode 2, a gate insulating layer 4, a semiconductor active layer 3, a source electrode 6, and a drain electrode 7. The gate electrode 2 and the gate line 1 are connected directly, and the source electrode 6 and the data line 5 are connected directly. A gate line protrusion 11 of the gate line 1 overlaps with the pixel electrode 10, which is for example made of indium tin oxide (ITO), and forms a storage capacitor with the pixel electrode 10. A passivation layer 8 covers the surface of the array substrate, and the drain electrode 7 of the TFT is connected with the pixel electrode 10 through a via hole 9. A scanning signal provided through the gate line 1 to the gate electrode 2 turns on/off the TFT, and a data signal provided through the data line 5 to the source electrode 6 is transmitted via the channel of the TFT to the drain electrode 7 and the pixel electrode 10 connected therewith. The resistance of the gate line 1 affects the loss and delay of signal during signal transmission.
In the LCD described above, a higher reliability and a more competitive power can be obtained by forming electrodes with metal materials of low resistivity and high corrosion-resistance. Typically, metal Al or Al alloys are widely used as the materials for forming metal wires and electrodes in a LCD. However, as the liquid crystal TV sets are becoming popular, LCDs are becoming larger in size and the definition standard also is becoming higher, which require the timing for scanning signal shorter and signal transmission rate of metal wires increasingly faster. To meet these requirements, it is necessary to explore a new metal material with lower resistivity to replace Al and Al alloys to form wires and electrodes to transmit signal. Compared with aluminum (Al), metal copper (Cu) has lower resistivity and higher electro-migration resistance so as to be a suitable substitute metal material. The parameters of various metals are shown in Table I.
TABLE IResistivity(μΩ · cm)HeatMetalBulkThin FilmAdhesionResistanceAg1.586N/APoorPoorCu1.6782PoorGoodAu2.43PoorGoodAl2.65484GoodPoorMo5.210GoodGoodW5.6512GoodGoodCr12.925GoodGoodTi4250GoodGood
However, metal Cu has a weak adhesion to glass, has a high diffusivity in silicon and oxides thereof, and is prone to be naturally oxidized, which makes metal Cu unsuitable to be used for scanning wires in a single-layered metal thin film. In general, metal Cu is used along with a blocking layer formed by one or two layers of other metal films, with the blocking layer being interposed between the glass substrate and metal Cu as well as between metal Cu and a semiconductor thin film. The blocking layer can improve the adhesion of the Cu wire to glass, and can also prevent Cu from diffusing into the semiconductor thin film.
A TFT with metal Cu wires and electrodes can be applied to LCDs so as to improve aperture ratio and image quality of the LCDs. A LCD can be manufactured by a conventional five-mask (5 Mask) technology, as shown in FIGS. 2a-2e. 
A metal Cu thin film is deposited on a glass substrate 100 as a gate metal layer, and a gate electrode 2 and a gate line 1 connected together are formed by a wet etching method with a gate mask. FIG. 2a shows a cross-sectional view of the gate electrode 2 through line A-A of FIG. 1. A gate insulating layer 4 and a semiconductor active layer 3 such as an amorphous silicon layer are deposited successively on the gate metal, and a semiconductor active layer 3 is formed into an island with an active layer mask, as shown in a cross-sectional view in FIG. 2b. A source/drain metal thin film is deposited, and a source electrode 6, a drain electrode 7 and a data line 5 are formed with a source/drain electrode mask, as shown in a cross-sectional view in FIG. 2c. A passivation film is deposited, and a passivation layer 8 and a via hole 9 in the passivation layer 8 are formed with a passivation layer mask, as shown in a cross-sectional view in FIG. 2d. A transparent conductive thin film is deposited, and a pixel electrode 10 is formed with a pixel electrode mask and connected with the drain electrode 7 through the via hole 9, as shown in a cross-sectional view in FIG. 2e. 
TFTs and LCDs utilizing metal Cu electrodes and wires are disclosed in U.S. Pat. Nos. 6,686,661, 6,727,188, 6,780,784, 6,858,479, 6,861,368, 6,881,679, 6,961,101, and 7,052,993. In case that metal Cu is used for the gate line 1 and gate electrode 2, the data line 5, the source electrode 6, and the drain electrode 7, a gate line formed in a multilayered thin film containing Ti, Ta, Mg, Mo, Ag, In or Cr is generally utilized, and a blocking layer and a diffusion-preventing layer are provided above and below the metal Cu thin film, respectively. Since metal Cu is different from metal Al, it is necessary to develop suitable etching solutions and make the etching rates of the metal of the blocking layer and the metal of the diffusion-preventing layer to match that of metal Cu, so as to facilitate forming the pattern of the wires and electrodes of the TFT. Suitable etching solutions in various cases are shown in Table II.
TABLE IIGate Metal AlloyEtching Solution(s)Cu, Cu/Ti, Cu/TaCu(OOC)4, CuSO4, MxSO3/MxS2O3/MxS2O4Cu/Ti, or Cu/MoH2O2, CH3COOH, H2SO4/HNO3/HCl/H3PO4,KCl/NaCl/KHSO4Cu/Ti2KHSO5•KHSO4•K2SO4, HF, NH4F, KHF2,Na2SO3/K2SO3/(NH4)2SO3, (NH4)2SO3
As shown in Table II, U.S. Pat. Nos. 6,727,188, 6,780,784, and 6,881,679 have disclosed some etching solutions for metal Cu and can obtain a stable etching rate. U.S. Pat. Nos. 6,686,661, 6,858,479, 6,861,368, 6,961,101, and 7,052,993 also form wires and electrodes of a metal Cu thin film with a blocking layer of other metals as well as wires and electrodes of Cu alloys. For example, U.S. Pat. Nos. 6,686,661 and 7,052,993 use a blocking layer of Mg, U.S. Pat. No. 6,858,479 forms wires with Ag/Cu thin film by plating, and U.S. Pat. No. 6,961,101 uses electrodes of Cu—In alloy. The above-mentioned patents proposed one or more materials for the metal blocking layer, or proposed one or more Cu alloys, which requires forming Cu wires and electrodes with different etching solutions. If the components for the blocking layer or the Cu alloy changes, it is necessary to develop a new etching solution, which results in increase of cost during development and manufacture. Furthermore, the fact that the manufacturers use different metals or alloys will also increase the cost of the etching solutions.